Seriously, this is the only game where I feel I'm battling demons. Like, actually evil hellspawns. Yeah, you have Doom and whatnot, but demons are supposed to be cunning, vicious, depraved... For a game to nail this so well, it must not only construct a good story, but the rest of the delivery must be near perfect too.
That sinking, ominous feeling when you fall for a trap or make a stupid decision with permanent consequences... That's not something just anyone can make. It's not the trap itself, it's every line of dialog, the build-up only such carefully crafted characters can make.
The only other piece of media that could convey this demonic dread to me was Berserk's ending. But, due to the demons being able to corrupt the mind itself, this game feels not only more... well, demonic, but a lot deeper as well.
Haven't found anything quite like it.